Examples of such gas sensors are infrared optical and electrochemical gas sensors as well as catalytic heat tone sensors. Within their housings, these gas sensors have a measuring cell, in which the gases to be measured are detected on the basis of physical or chemical processes. Depending on the conditions of use, regular calibration with a calibrating gas of known concentration is to be performed for the operation of such gas sensors. According to the current state of the art, this is carried out, as a rule, by pulling a calibrating adapter, which is flushed with a known calibrating gas, for example, from a pressurized gas cylinder, over the gas sensor for each calibration. To be independent from the wind in the measuring environment during the calibration, the calibrating adapter is gas-tight to the calibrating gas, except for the connection of the gas cylinder and a small opening for the discharge of the gas.
Such a prior-art calibrating adapter for an electrochemical gas sensor is described, for example, in U.S. Pat. No. 4,742,708. One drawback of the prior-art calibrating adapter is that free diffusion of the gas to the measuring cell is prevented by the calibrating adapter itself, so that the calibrating adapter is placed on the gas sensor for the duration of the calibration only and must subsequently be removed in an additional operation. This is associated with manual effort and consequently costs especially in case of stationarily installed gas sensors at poorly accessible measuring sites or under difficult environmental conditions involving exposure to wind or health hazard.